C 语言 typeof 关键字

如何结合使用 C 语言关键字 typeof 实现一个栈结构？下面这段代码使用双向链表实现一个栈：

#define StackInit(s) ((s)->prev = (s)->next = (s))
#define StackEmpty(s) ((s)->next == (s))
#define StackPush(s, ptr) ({ \
    (s)->prev->next = (ptr); \
    (ptr)->prev = (s)->prev; \
    (s)->prev = (ptr); \
    (ptr)->next = (s); })
#define StackPop(s) ({ \
    typeof(s) top = (s)->prev; \
    (s)->prev->prev->next = (s); \
    (s)->prev = (s)->prev->prev; \
    top->next = top->prev = 0; \
    top; })

typedef struct StackItem {
    struct StackItem *prev;
    struct StackItem *next;
} StackItem_t;

实际使用示例，可以看到，这个简单的栈是个通用构造，Linux 内核中有很多类似的代码。

#define OFFSETOF(type, member) ((size_t)&((type*)0)->member)
#define CONTAINEROF(ptr, type, member) ( \
    (type*)((char*)ptr - OFFSETOF(type, member)))

typedef struct SElem {
    int ord;
    struct StackItem node;
} SElem_t;

#define SElemEntry(ptr, type, member) CONTAINEROF(ptr, type, member)

int main()
{
    StackItem_t s;
    StackInit(&s);

    SElem_t item;
    StackPush(&s, &item.node);

    StackItem_t *e = StackPop(&s);
    SElem_t *x = SElemEntry(e, SElem_t, node);

    // x:0x7fff55e59b00 item:0x7fff55e59b00
    printf("x:%p item:%p\n", x, &item);
    
    return 0;
}   

参考资料：

• typeof 关键字
• 逗号运算符

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This work is licensed under a MIT License.

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